Abstract

The financial costs of defoliation of Scots pine by the pine looper moth (Bupalus piniaria L.) were evaluated for three pine stands in Tentsmuir Forest, Scotland, by comparing observed tree growth with estimates of the growth that would have been expected if the moth had not been present. It was calculated that five or seven periods of partial defoliation, caused by successive peaks in the moth population, had reduced the total volume of marketable timber available in thinnings and at final harvest by 26-35 m(3) ha(-1). Nearly all of this loss occurred in the sawlog category of timber. Total discounted income over the rotation, based on long-term (1984-2001) average timber prices and a 3.5 per cent discount rate, was reduced by 5.8-7.5 per cent when the same rotation length was used for both observed and expected growth. At a discount rate of 6 per cent, total income was reduced by 4.4-5.2 per cent. Extending the rotation by 3 or 4 years to allow the mean final tree size to reach that expected in the absence of defoliation, or by 4 or 6 years to allow the same total volume of timber to be extracted, increased total revenue but did not increase gross discounted income because of the effect of discounting over a greater number of years.